1. Technical Field
The present invention relates to a physical quantity sensor, an electronic device, and a moving object.
2. Related Art
Currently, for various systems or electronic devices, physical quantity sensors capable of detecting various physical quantity items, such as an acceleration sensor for detecting acceleration or a gyro sensor for detecting angular velocity, have been widely used. In recent years, since the various physical quantity sensors are mounted on a vehicle, extremely high reliability has been required.
For example, a gyro sensor using a piezoelectric vibrator may have a slight crystal defect of a sensor element or a slight damage such as a microcrack occurring in a manufacturing step, and the sensor element may be damaged over time due to the defect or the damaged portion. It is difficult to detect all defects in inspection of electrical properties before shipping, and accordingly it is normal to have a burn-in test for the gyro sensor for a vehicle market in which high reliability is required, in order to detect the damage to the element, in addition to the general test for the electrical properties. In the defect detection of such an element, a method called overdriving for increasing a drive level of the piezoelectric vibrator to a higher level than a level normally used, is generally used.
JP-A-2001-07648 discloses a configuration of a piezoelectric oscillator which includes a constant voltage circuit between a power supply and an oscillating circuit, and is configured so as to supply a constant voltage to the oscillating circuit, in which the constant voltage circuit can be set to be invalid. According to this piezoelectric oscillator, since the constant voltage circuit can be set to be invalid, it is possible to change a drive level by changing a power supply voltage.
JP-A-2004-120523 discloses a crystal oscillator capable of performing quality determination from a frequency change amount due to change in capacity of an external load capacitor, by attaching an external load capacitor with a variable capacity value to an oscillating circuit. According to this crystal oscillator, it is not necessary to provide an additional circuit for setting a function of the constant voltage circuit to be invalid.
JP-A-2004-328505 discloses a piezoelectric oscillator capable of separating a piezoelectric vibrator and an oscillating circuit by providing a switch circuit between the piezoelectric vibrator and the oscillating circuit. According to this piezoelectric oscillator, when performing an overdriving process used for removal of foreign body, the piezoelectric vibrator and the oscillating circuit can be separated from each other and accordingly, it is possible to prevent damage to the oscillating circuit due to high voltage application.
However, since the physical quantity sensor such as the gyro sensor may have an auto gain control (AGC) circuit which is embedded therein for maintaining constant output sensitivity, and the overdriving process is difficult to perform even when a higher power supply voltage than usual is applied, the drive level of the sensor element does not change even when the method disclosed in JP-A-2001-07648 or JP-A-2004-120523 is applied as it is. Accordingly, since the time required for the burn-in test is long, it is difficult to reduce test cost and it is also difficult to evaluate drive level properties. In addition, in the method disclosed in JP-A-2004-328505, since it is necessary to apply an AC voltage having large amplitude from the outside, the application to a tuning fork type vibrator using bending vibration may be merely a breakdown test.